Algorithmic Thinking and Structured Programming (in Greenfoot) Teachers: Renske Smetsers-Weeda Sjaak Smetsers Ana Tanase

Transcription

1 Algorithmic Thinking and Structured Programming (in Greenfoot) Teachers: Renske Smetsers-Weeda Sjaak Smetsers Ana Tanase

2 Today s Lesson plan (4) 20 min Quiz 10 min Looking back What did we learn last week? Discuss problems / homework (and handing-in) Blocks of theory and exercises / unplugged 10 min Wrapping up Next class: Fri Jan 8 th (NOT next week)

3 Swap Puzzle level 3 Describe a strategy In Java: square1 = square2; Which means: square 1 getspiecefrom square2

4 Swap Puzzle level 3

5 Computational thinking Working in a structured manner: Breaking problems down into subproblems Design, solve and test solutions to subproblems Combing these (sub)solutions to solve problem Analyzing the quality of a solution Reflecting about the solution chosen and proces Generalizing and re-use of existing solutions

6 Discuss problems / homework Only hand in (via ): MyDodo.java Document with answers to only (IN) questions Any problems? Please !

7 Sequence flowchart code public methodname( ) { step1(); step2(); step3(); }

8 Selection (choice, if..then..else) public methodname( ) { flowchart code } if( check () ) { step1a(); }else{ step1b(); }

9 Repetition (iteration, loop) flowchart code public methodname( ) { while ( check () ) { dosomething (); } }

10 Challenge & problem You must perform two aspects well: 1) Create a problem-solving algorithm (a disciplined and creative process) We use a systematic approach 2) Formulate that algorithm in terms of a programming language (a disciplined and very precise process) Always check that your algorithm is correct by running/testing the implementation!

11 Today: Greenfoot Run: Act in a while loop Greenfoot.stop() Parameters Submethods: a method call in a method Boolean expressions (NOT, OR, AND)

12 Greenfoot Run Run is a special Greenfoot feature Run: Act called repeatedly Act in a while loop

13 >Run: built in iteration Can only be interrupted by: - Pressing Pause - Calling Greenfoot.stop()

14 >Run: calling act repeatedly What if your void act() contains a while-loop? Example: hatching a row of eggs

15 Iteration in act ACT Start Initial situation False NOT Border Ahead move True foundegg True False hatchegg End Final situation

16 Act in Run RUN False ACT Start NOT Stop NOT Border Ahead move True True One loop is superfluous Try to eliminate the act loop: Keep your act as simple/small as possible. foundegg True False hatchegg End

17 No iteration in act ACT Start False Greenfoot.stop NOT Border Ahead True move foundegg False hatchegg End

18 The golden-promise: Don t put too much work in the act method. Avoid time-consuming while-loops or while-loops with visible effects.

19 JAVA: Printing to screen(console) Printing text to the screen (console) with: System.out.println ( Hello ); Print a variable studentname to the screen with: System.out.println ( studentname); Print a combination of text and variable: System.out.println ( Hello + studentname); Example code: studentname = Jack ; System.out.println ( Hello + studentname); Outputs to screen: Hello Jack

20 Unplugged Songwriting Parameters Submethods

21 Songwriting: Parameters & Submethods Old MACDONALD had a farm E-I-E-I-O And on his farm he had a cow E-I-E-I-O With a moo moo here And a moo moo there Here a moo, there a moo Everywhere a moo moo Old MacDonald had a farm E-I-E-I-O. Song goes on for (just about) ever

22 More generic: Finding parameters Old MACDONALD had a farm E-I-E-I-O And on his farm he had a cow E-I-E-I-O With a moo moo here And a moo moo there Here a moo, there a moo Everywhere a moo moo Old MacDonald had a farm E-I-E-I-O Old MACDONALD had a farm E-I-E-I-O And on his farm he had a <ANIMAL> E-I-E-I-O With a <SOUND> <SOUND> here And a <SOUND> <SOUND> there Here a <SOUND>, there a <SOUND> Everywhere a <SOUND> <SOUND> Old MacDonald had a farm E-I-E-I-O

23 More generic: Using parameters Old MACDONALD had a farm E-I-E-I-O And on his farm he had a <ANIMAL> E-I-E-I-O With a <SOUND> <SOUND> here And a <SOUND> <SOUND> there.. Old MacDonald had a farm E-I-E-I-O System.out.println( Old MACDONALD had a farm ); System.out.println( E-I-E-I-O ); System.out.println ( And on his farm he had a + animal ); System.out.println( E-I-E-I-O ); System.out.println( With a + sound + + sound+ here ); System.out.println( And a + sound + + sound + there ) System.out.println( Old MACDONALD had a farm ); System.out.println( E-I-E-I-O );

24 Introducing parameters

25 Generic: Using parameters

26 More generic: finding repetition Old MACDONALD had a farm E-I-E-I-O And on his farm he had a cow E-I-E-I-O With a moo moo here And a moo moo there Here a moo, there a moo Everywhere a moo moo Old MacDonald had a farm E-I-E-I-O

27 Defining submethods [1] public void printoldmchadfarm ( ) { } System.out.println( Old MACDONALD had a farm ); public void singoldmcdonaldchorus ( String animal, String sound ) { } printoldmchadfarm ( ); System.out.println( "E-I-E-I-O" ); System.out.println( "And on his farm he had a " + animal ); System.out.println( "E-I-E-I-O" );

28 Why submethods [1]: easy to change Change in 1 place From: public void printoldmchadfarm ( ) { System.out.println( Old MACDONALD had a farm ); } Into: public void printoldmchadfarm ( ) { System.out.println( Old McDonald had a farm ); }

29 Defining submethod with arguments public void printhadanimal ( String animal ) { } System.out.println( And on his farm he had a + animal ); public void singoldmcdonaldchoruss ( String animal, String sound ) { } printoldmchadfarm(); printeieio(); printhadanimal ( animal ); printeieio (); printoldmchadfarm(); printeieio ();

30 Why submethods [2]: easy to read public void singoldmcdonald ( String animal, String sound ) { } printoldmchadfarm(); printeieio(); printhadanimal ( animal ); printeieio (); printwithsound (sound ); printandsound (sound ); printoldmchadfarm(); printeieio ();

31 Why submethods and arguments More generic: Less code Less mistakes Easier to read / understand Code can be used for more ( animals) Easier to change Easier to reuse

32 Your turn! The wheels on the bus go round and round, round and round, round and round. The wheels on the bus go round and round, all through the town. The doors on the bus go open and shut. The wipers on the bus go Swish, swish, swish On paper: Find parameters and replace text Find and use submethods Write method to print song using parameters & submethods

33 Boolean quiz Answer questions on paper (incl your name) Hand-in Papers will be shuffled Teacher chooses paper and reads last statement If this is you. DON T SAY A THING Everyone stands Teachers reads statements: If True about you: stay standing If False about you: sit down

34 Answer the following 1. What is your favorite number? 2. What is the color of your bicycle? 3. What is your favorite color? 4. What month were you born? 5. Do you have siblings? 6. What is the last digit of your phone number? 7. What is something about you that people here don t know and can t tell by looking at you?

35 Boolean Quiz

36 Boolean statements What it s about: In English, an or is often an exclusive or such as You can have chicken or fish. In English, you only get to pick one But with Boolean logic you could have chicken, fish, or both!! A B means: (A or B) or (A and B)

37 True or False? Booleans can be true or false Boolean statements can be made very complex using combinations: NOT:! AND: && OR: For example: (A B) &&! ( (A && B) C ) Careful: Often a source of errors!

38 Modifying code After each MINOR adjustment Compile Test if it still works If you do too much at once, and then get an error you re doomed to get frustrated! Remember, from our first lesson: Expect to make mistakes! Learn from them.

39 Computational thinking Working in a structured manner: Breaking problems down into subproblems Design, solve and test solutions to subproblems Combing these (sub)solutions to solve problem Analyzing the quality of a solution Reflecting about the solution chosen and proces Generalizing and re-use of existing solutions

40 Questions?

41 Wrapping up Homework for Wednesday 8:30 Jan.6 th 2016: Assignment 3: finish Assignment 4 up to and incl Hand in: Via MyDodo.java and IN to Renske.weeda@gmail.com (Flowcharts: op paper in pigeonhole or photo/scan and paste into document)